The invention relates to a train protection and control system in which at least one transmitter is provided at the railway right-of-way for the transmission of orders necessary in controlling train traffic and for the wireless exchange of general information between a track control center and trains moving in the associated right-of-way section, with a data processing unit being disposed at the track control center and providing a cyclic determination of control orders.
Electrical train reporting systems have been employed in railroad systems, in which orders necessary for the control of the train operations are transmitted by radio. In some installations the exchange of information between the train and right-of-way takes place linearly and in order to determine the location of the trains and for an exchange of information between such trains and a track control center, a line is placed along the right-of-way which is permanently fed with an AC voltage from the track control center, over respective marking points. Such line comprises a pair of unshielded conductors which are crossed at regular intervals whereby they change their position along the track. The crossing points thus formed can be "identified electrically" from the trains by means of inductively coupled receiving coils, the location of the train being determined by counting the respective crossing points.
The corresponding counting result, or intermediate results, can be reported over the line to the track control center, in order to determine additional control orders necessary for proper train movement. Such control orders are determined cyclically at the track control center by a data processing unit and thus regularly issued over the line and received on the trains by means of receiving coils inductively coupled with such line. The transmission of data in such cases is accomplished in accordance with the known principle of holding current. The orders issued by the track control center for reception and evaluation on board the rail vehicles are so designed that even a very short interruption in the transmission of data is identified as a defect and will result, for example, in a positive braking operation. This arrangement insures that a train in motion which is controlled by such a system involving linear train control, can be informed at a given time from the track control center, about changes in operation conditions. This only insures that limited operating orders can be transmitted with certainty to the trains. In other words, it is insured that the installations protecting the train traffic will have access to the moving trains at all times, even with linear exchange of information between the trains and the track control center.
While the use of avilable radio channels for the transmission of the necessary traffic control orders from a control center to the moving trains without the use of a line, the above-described principle of holding current is not feasible as the known train radio channels occasionally exhibit so-called transmission gaps resulting from atmospheric disturbances or unfavorable topography, whereby the transmission of orders to the trains is interrupted or even impossible. However, the density of information of stationary or variable data of a track section is so low that the low volume of information of the available railroad radio channels is adequate over and above train protection. However, it will be noted in this connection that the known railroad radio channels, i.e., the transmitters along the right of way and the receiving installations on board the trains will be used to a large extent for two-way communication. As a result, orders to be transmitted for train traffic control to the traction vehicles cannot be transmitted continuously, but rather only when a change in orders is involved. In the interim, the railroad radio channels are available for operational functions such as two-way radio communication.
With such an economical utilization of the available railway radio channels, no assurance exists, without problems, that in the event of a change of the operational conditions, especially in the event of a restriction, that the affected train can be informed without delay, as it is not known whether the entire transmission system is in a state of operational readiness for transmission of the required order.
Consequently, the invention is directed to the problem of so supplementing an installation of the type initially described that the radio type control will be effected in a manner similar to a holding current operation and which may be accomplished with a low rate of data for the control of the train traffic, whereby the operational functions involved in the train radio traffic control will not be impeded even though the operation does not actually involve a holding current.